Why can the temperature drift of thick film resistors only reach a minimum of 100ppm?
In the field of electronic design, thick film resistors are one of the most widely used components, known for their low cost, high power, and complete specifications. But in precision circuit design, engineers often face a ceiling: why is the temperature drift (TCR) of the vast majority of ordinary thick film resistors on the market usually labeled as 100ppm/℃ or higher? Even thick film resistors with certain precision seem to have their temperature drift limit stuck around the threshold of 100ppm.
To understand this issue, it is necessary to delve into the internal structure and conductivity mechanism of thick film resistors.
Material properties: Innate genes of thick film resistors
The core of thick film resistors is conductive paste, mainly composed of a mixture of metal oxides such as ruthenium dioxide and glass glaze. This slurry is sintered at high temperatures to form a complex granular glass matrix structure. Electric current is not transmitted through continuous metal conductors, but rather jumps forward through the "contacts" between conductive particles.
This particle structure leads to two problems: on the one hand, the conductive channels are unstable, and when heated, the glass matrix expands or contracts, causing changes in the spacing between conductive particles and drastic fluctuations in resistance; On the other hand, thick film resistors are sensitive to temperature changes, and the temperature coefficient of resistance is usually difficult to reduce.
In contrast, the conductive material of thin film resistors or foil resistors is uniform and continuous, and the resistance changes very little when heated and expanded. Since the birth of thick film resistors, the material system has determined that their temperature drift is difficult to achieve as easily as thin film resistors at 10ppm or lower.
Process and Cost: Commercial Balance Point of 100ppm
Technically speaking, by adjusting the slurry formula and sintering process, thick film resistors below 100ppm can indeed be produced. For example, Fenghua High tech uses copper nickel alloy slurry and nitrogen protection sintering process to control the temperature drift of thick film resistors in specific low resistance ranges within ± 100ppm. Some precision thick film resistors can even reach ± 50ppm or better.
But the problem is that this is no longer a typical category of "ordinary thick film resistors". When thick film resistors attempt to break through the 100ppm temperature drift, the process difficulty will sharply increase - extremely precise control of sintering temperature, time, and atmosphere is required, and the yield rate is difficult to guarantee, resulting in exponential cost growth.
Once the temperature drift requirement enters the range of ± 50ppm or even ± 25ppm, designers will prioritize choosing thin film resistors or metal foil resistors. These technologies perform better in terms of temperature drift and long-term stability, and their cost is not much higher than high-precision thick film resistors when produced in large quantities. Therefore, 100ppm has become the default watershed in the thick film resistor industry: it is the optimal balance point between universality and economy.
Considerations in practical applications
Thick film resistors have the advantages of high voltage resistance, moisture resistance, and high power density. If the project does not require high absolute accuracy or has a software calibration mechanism, a 100ppm thick film resistor is completely sufficient and cost-effective. But if pursuing the temperature stability of the product, forcibly selecting thick film resistors below 100ppm is not a wise move.
For scenarios with high precision and low temperature drift requirements, it is recommended to directly use thin film resistors. On the market, various precision resistor product lines represented by Shenzhen Shunhai Technology Co., Ltd. are complete and can provide professional technical selection support. Through authorized channels such as Huanian Mall, it is easy to purchase thick film resistors and high-precision thin film resistors from brands such as Tian'er and Lizhi.
In summary, the temperature drift of thick film resistors remains at 100ppm, which is essentially the result of the game between material physical limits and industrial costs. At the 100ppm node, thick film resistors maintain the highest cost performance ratio.
